The present invention relates to the external control of the flow rate of a constant flow fluid delivery device and more particularly to the external control of an implantable constant flow medication infusion pump.
There are two basic types of implantable pumps: constant flow pumps and programmable rate pumps. In the constant flow (or passive) pump, the flow rate is fixed, so in order to control the amount of medication delivered, the clinician must set the concentration of the medication taking into account the fixed flow rate of the pump. Patients needing changes to their medication delivery rate must visit their physician, who removes the remaining medication in the reservoir, and replaces it with a medication at a different concentration. U.S. Pat. No. 5,836,915 issued Nov. 17, 1998 for xe2x80x9cImplantable Infusion Pumpxe2x80x9d describes such a constant flow pump that comprises two chambers divided by a flexible membrane. The pump described in the ""915 patent includes a first chamber containing the medication to be pumped, and a second chamber containing a motive substance. The motive substance creates pressure in the second chamber that is transferred to the first chamber by the membrane. The motive substance is selected so that the pressure remains constant, and therefore the rate of the resulting medication flow remains constant also.
Alternatively, programmable pumps can provide variable flow rates. Programable pumps may deliver the medication either by solenoid pump or by peristaltic pump. In the solenoid pump, the flow rate can be controlled by changing the stroke rate of the pump. In the peristaltic pump, the flow rate can be controlled by changing the roller velocity. Disadvantageously, both types of programmable pumps generally require a battery and sophisticated controllers to enable their operation and control.
A pump could be made utilizing a cable passing through the skin to control the pumping rate. However, a cable connection through the skin of the patient interferes with the freedom of movement of the patient, and represents a possible source of infection.
Therefore, there is a need for a constant flow pump with a means for varying its flow rate, that overcomes the limitations of the existing constant flow pumps without the complexity of the existing programable pumps, and avoids using a control cable that passes through the skin.
The present invention addresses the above and other needs by providing an externally controllable constant flow medication delivery system that retains the simple robust features of a constant flow pump, while providing a capability to adjust flow rates. The system utilizes an external control device and an implantable pump. The implantable pump includes a constant flow pump and a controllable flow regulator. Flow rate commands are provided to the implantable pump from the external control device via an RF link. An actuator is mechanically connected to the flow regulator, and mechanically adjusts the flow regulator each time a new flow rate is commanded. The power required by the actuator to execute flow rate changes is also provided via the same RF link.
It is a feature of the present invention to provide an implantable pump with a flow rate that may be adjusted by an external device. The capability to easily alter the medication flow rate allows a physician to maintain a single or small inventory of medication concentrations for refilling the implantable pump, and alleviates the need to remove medication of one concentration and refill with medication of another concentration when a change in delivery rate is required.
It is another feature of the present invention to provide control signals over an RF link. Such RF link avoids the use of a cable through the skin and the discomfort and risk of infection that may result from a cable through the skin.
It is yet another feature of the present invention to provide an implantable pump with the simplicity of a constant flow rate pump, simple electronics, and no requirement for a battery. Advantageously, such a simple pump provides both durability and reduced cost.
In accordance with another aspect of the present invention, the only power required by the implantable pump is the power needed to change the flow rate. Advantageously, that power is provided by an external control device over an RF link. Therefore, the implantable pump requires no internal power source.
It is a further feature of the present invention to encode a unique serial number on the transmitted flow rate commands. This unique serial number functions as a password so that only intentional flow rate changes are executed by the implantable pump.
It is an additional feature of the present invention to provide back telemetry from an implantable pump to an external control device. The back telemetry provides a means through which data may be sent to the external control device. Such data may include system status information, e.g., confirmation that the flow rate command had been executed, pressure, present flow rate, or other instantaneous measurements.